214 research outputs found
Magnetic field detection in the B2Vn star HR 7355
The B2Vn star HR 7355 is found to be a He-rich magnetic star.
Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory
to measure the disk-averaged longitudinal magnetic field at various phases of
the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z
= -2200 and +3200G was found, with confidence limits of 100 to 130G. The field
topology is that of an oblique dipole, while the star itself is seen about
equator-on. In the intensity spectra the HeI-lines show the typical equivalent
width variability of He-strong stars, usually attributed to surface abundance
spots. The amplitudes of the equivalent width variability of the HeI lines are
extraordinarily strong compared to other cases. These results not only put HR
7355 unambiguously among the early-type magnetic stars, but confirm its
outstanding nature: With v sin i = 320 km/s the parameter space in which
He-strong stars are known to exist has doubled in terms of rotational velocity.Comment: 6 pages, 5 figures, 1 Table. Accepted for publication in MNRAS
Letter
Cyclic Variability of the Circumstellar Disc of the Be Star Tau. II. Testing the 2D Global Disc Oscillation Model
Aims. In this paper we model, in a self-consistent way, polarimetric,
photometric, spectrophotometric and interferometric observations of the
classical Be star Tauri. Our primary goal is to conduct a critical
quantitative test of the global oscillation scenario. Methods. We have carried
out detailed three-dimensional, NLTE radiative transfer calculations using the
radiative transfer code HDUST. For the input for the code we have used the most
up-to-date research on Be stars to include a physically realistic description
for the central star and the circumstellar disc. We adopt a rotationally
deformed, gravity darkened central star, surrounded by a disc whose unperturbed
state is given by a steady-state viscous decretion disc model. We further
assume that disc is in vertical hydrostatic equilibrium. Results. By adopting a
viscous decretion disc model for Tauri and a rigorous solution of the
radiative transfer, we have obtained a very good fit of the time-average
properties of the disc. This provides strong theoretical evidence that the
viscous decretion disc model is the mechanism responsible for disc formation.
With the global oscillation model we have successfully fitted spatially
resolved VLTI/AMBER observations and the temporal V/R variations of the
H and Br lines. This result convincingly demonstrates that the
oscillation pattern in the disc is a one-armed spiral. Possible model
shortcomings, as well as suggestions for future improvements, are also
discussed.Comment: 14 pages, 9 figures, accepted to A&
A Novel p.Leu(381)Phe Mutation in Presenilin 1 is Associated with Very Early Onset and Unusually Fast Progressing Dementia as well as Lysosomal Inclusions Typically Seen in Kufs Disease
Whole exome sequencing in a family with suspected dominant Kufs disease identified a novel Presenilin 1 mutation p.Leu(381)Phe in three brothers who, along with their father, developed progressive dementia and motor deficits in their early 30s. All affected relatives had unusually rapid disease progression (on average 3.6 years from disease onset to death). In silico analysis of mutation p.Leu(381)Phe predicted more detrimental effects when compared to the common Presenilin 1 mutation p.Glu(280)Ala. Electron microscopy study of peripheral fibroblast cells of the proband showed lysosomal inclusions typical for Kufs disease. However his brain autopsy demonstrated typical changes of Alzheimer disease
Optical variabilities in Be/X-ray binary system:GRO J2058+42
We present an analysis of long-term optical monitoring observations and
optical spectroscopic observations of the counterpart to CXOU J205847.5+414637
(high mass X-ray binary system). We search for a variability in the light curve
of Be star. We used differential magnitudes in the time series analysis. The
variability search in the optical light curve was made by using different
algorithms. The reduction and analysis of spectra were done by using MIDAS and
its suitable packages. We have performed a frequency search which gave us the
value 2.404 1/day. This value is attributed to the non-radial pulsation of Be
star. H alpha emission line profiles always show double-peaked emissions with a
mean equivalent width of 2.31 \pm 0.19 \AA ~and a peak separation of 516 \pm 45
km/s. This suggests that Be star disk is still present. CXOU J205847.5+414637
is in X-ray quiescent state.Comment: 8 pages, 9 figures. To appear at Astronomy and Astrophysic
School librarians as literacy educators within a complex role
Librarians in schools are expected to play an important role as literacy educators, and have a positive impact on young people’s literacy learning. However in the context of their diverse workload, relatively little is known about how this aspect of their role sits within its competing demands, and the exact scope of the literacy educator requirements. Using a hybrid approach to content analysis, this article analyses 40 recent job description documents to identify the nature and prevalence of different aspects of the role, and to explore the literacy educator aspect of this profession. Findings suggest that while the literacy educator aspect is one of the most common role requirements, it sits within a complex workload, and the literacy educator aspect is itself multi-faceted and demanding
Imaging the heart of astrophysical objects with optical long-baseline interferometry
The number of publications of aperture-synthesis images based on optical
long-baseline interferometry measurements has recently increased due to easier
access to visible and infrared interferometers. The interferometry technique
has now reached a technical maturity level that opens new avenues for numerous
astrophysical topics requiring milli-arcsecond model-independent imaging. In
writing this paper our motivation was twofold: 1) review and publicize
emblematic excerpts of the impressive corpus accumulated in the field of
optical interferometry image reconstruction; 2) discuss future prospects for
this technique by selecting four representative astrophysical science cases in
order to review the potential benefits of using optical long baseline
interferometers. For this second goal we have simulated interferometric data
from those selected astrophysical environments and used state-of-the-art codes
to provide the reconstructed images that are reachable with current or
soon-to-be facilities. The image reconstruction process was "blind" in the
sense that reconstructors had no knowledge of the input brightness
distributions. We discuss the impact of optical interferometry in those four
astrophysical fields. We show that image reconstruction software successfully
provides accurate morphological information on a variety of astrophysical
topics and review the current strengths and weaknesses of such reconstructions.
We investigate how to improve image reconstruction and the quality of the image
possibly by upgrading the current facilities. We finally argue that optical
interferometers and their corresponding instrumentation, existing or to come,
with 6 to 10 telescopes, should be well suited to provide images of complex
sceneries.Comment: Acccepted to Astronomy and Astrophysics Revie
Detection of a Hot Subdwarf Companion to the Be Star FY Canis Majoris
The rapid rotation of Be stars may be caused in some cases by past mass and
angular momentum accretion in an interacting binary in which the mass donor is
currently viewed as a small, hot subdwarf stripped of its outer envelope. Here
we report on the spectroscopic detection of such a subdwarf in the Be binary
system FY Canis Majoris from the analysis of data acquired by the IUE
spacecraft and KPNO Coude Feed Telescope over the course of 16 and 21 years,
respectively. We present a double-lined spectroscopic orbit for the binary
based upon radial velocities from the IUE spectra and use the orbital solutions
with a Doppler tomography algorithm to reconstruct the components' UV spectra.
The subdwarf is hot (T_eff = 45+/-5 kK) and has a mass of about 1.3 M_sun and a
radius of about 0.6 R_sun. It contributes about 4% as much flux as the Be star
does in the FUV. We also present observations of the H-alpha and He I 6678
emission features that are formed in the circumstellar disk of the Be star.
Orbital flux and velocity variations in the He I 6678 profile indicate that
much of the emission forms along the disk rim facing the hot subdwarf where the
disk is probably heated by the incident radiation from the subdwarf. A study of
the FUV infall shell lines discovered in the 1980s confirms their episodic
presence but reveals that they tend to be found around both quadrature phases,
unlike the pattern in Algol binaries. Phase-dependent variations in the UV N V
doublet suggest the presence of a N-enhanced wind from the subdwarf and a
possible shock-interaction region between the stars where the subdwarf's wind
collides with the disk of the Be star.Comment: 46 pages, 15 figures, ApJ in pres
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